This invention relates to current-limiting circuit interrupters, and more specifically relates to a novel adapter for a current-limiting circuit interrupter which permits the addition of one or more current-limiting breaks in series with the contacts of a conventional current-limiting breaker.
Current-limiting circuit breakers are well known in which the current in two contact arms flows in opposite directions in order to produce a magnetically derived force on the contacts which tends to separate the contacts when the current is greater than some predetermined magnitude. The contacts are then very rapidly opened against the force of a closing bias even before the contact operating mechanism has had a chance to move.
After the contacts open under the influence of the magnetic forces, the contact operating mechanism will eventually catch up with the contacts and latch the contacts in an open position. During the initial opening of the contacts, the arc drawn between them moves into an arc chamber. The arc voltage between the separating contacts then limits the current flowing through the circuit breaker and thus the fault current, and in most cases the current will be interrupted before the breaker operating mechanism is tripped. The interrupting capacity of such a breaker increases with the arc voltage which is produced.
It is well known that the interrupting capacity of a circuit interrupting system can be increased by adding additional series-connected breaks. Thus, U.S. Pat. No. 3,815,059 in the name of Spoelman discloses a molded case type circuit interrupter in which a first circuit breaker of conventional non-current-limiting type is connected in series with a second circuit breaker which may have current-limiting characteristics. In U.S. Pat. No. 3,815,059, however, both of the circuit breakers are provided with respective latch systems which latch the contacts open. The latches for both devices must then be reset or defeated in order to reclose the circuit breaker. Thus, at least two mechanisms must be operated in order to reclose the breaker with this prior art type of arrangement.